It is known that the conventional electric door, such as the rolling door or the garage door lifting and descending in vertical direction, or the rolling door rolling in horizontal direction, or the garage door opened and closed by rotating 90 degrees, or the other electrically operated doors, is typically designed with a latch device for jam in consideration of safety. However, ordinary user usually ignore it's existence, and start the door switch without releasing the latch device so that jamming happens between the door and the latch device. In the jammed condition, the door can not be opened, and the latch device can also not be released. There are a lot of disclosures relevant to the prevention of the fault operation of garage door, such as U.S. Pat. No. 5,684,372 and U.S. Pat. No. 5,841,253, etc., but these published disclosures employ the circuit control means to achieve the purpose.
In order to prevent the error start condition, the inventor of the present invention has filed the “DOOR OPENER ERROR-START PREVENTION DEVICE” in U.S. Pat. No. 6,900,602, for example, as shown in FIGS. 1a and 1b, it comprises: a door opener (20′) with one end having a base (21′) containing a space, and the other end accommodating a power unit (22′) for outputting power; an output shaft (24′), the first end (24a′) of which is formed with a center hole (241′) from the end top along the axial direction and this end is fixed at the center of end gear (23′) rotated by the power unit (22′), the second end (24b′) of which is partially extended and pivoted in the space of the base (21′), and formed with a pair of axial sliding slots (242′) from the periphery in the radial direction through the center hole (241′); a sprocket assembly (25′), which is invaginated at the second end (24b′) of the output shaft (24′) for free rotation, one end of the sprocket assembly (25′) having a sprocket (251′) which moves syschronously with the sprocket on the reel of the rolling door through a chain, the other end being integrally formed with a sleeve (252′), the periphery of the sleeve (252′) being formed with a pair of V-shaped slot (253′) which corresponds to the sliding slot (242′) on the output shaft (24′); a sliding pin (27′) being radially inserted in the sliding slot (242′) of the output shaft (24′) with two ends protruded into the V-shaped slot (253′) of the sleeve (252′); a compression spring (28′) being inserted in the center hole (241′) of the output shaft (24′), one end being fixed by the fastener (29′) and the other end being enforced against the sliding pin (27′); a swaying plate (30′) provided beside the sliding pin (27′), one end (30a′) of which-being fixed on the base (21′) and the other end being a free end (30b′); an obstacle sensing device (31′) provided beside the free end (30b′) of the swaying plate (30′). Under the condition of error start of door and the jam with latch device, the rotation of the door opener (20′) is stopped so that the torque of the sliding pin (27′) is limited. The sliding pin (27′) slides backward toward the direction of larger opening of the V-shaped slot (253′) and press the swaying plate (30′). This will trigger the obstacle sensing device (31′) to cut off the power of ascending circuit, and supply the reverse current for the door opener (20′) to rotate in opposite direction. The rolling door slides down and return to the original position.
In the above invention, an error start prevention device operated with mechanical force is provided, even under the error start condition along with jam between the door and the latch device, it can return actively to the original position. However, the person skilled in the art should understand that the pressure generated by the abutment of the compression spring (28′) against the sliding pin (27′) is deeply concerned with the trigger sensitivity of the sliding pin (27′). When the pressure is too small, the reaction of the sliding pin (27′) will become too sensitive, such that the circuit of obstacle sensing device (31′) has a early trip before the confirmation of the obstacle. On the contrary, when the pressure is too large, the reaction of the sliding pin (27′) will become relatively slow such that this may cause possible damage to the latch device. Thus, the pressure of the compression spring (28′) should be adjusted within an effective range. The inventor has considered that the only latch device (29′) in the above-mentioned mechanism for adjusting the pressure of the compression spring (28′) is located within the gear box (201′) of the door opener (20′), that is, when adjusting the pressure of the compression spring (28′), the door opener (20′) has to be disassembled. Therefore there is still some room for improvement.
Moreover, as shown in FIG. 1c, a sufficient clearance (d′) is maintained between the members of the normal latch device (40′) even under the condition of error start, the distance between the door leaving the lower stop point and the jam point, which corresponds to the clearance (d′). In the above invention, because the circuit of the obstacle sensing device (31′) is in serial connection with the normally closed contact of the lower limit switch of the door, when the door switch is activated, the normally closed contact of the lower limit switch will be opened after the door leaving the lower stop point. In order for the sensing device (31′) to maintain an effective detection distance, a conventional delay circuit is employed to extend the time corresponding to the effective detection distance, so that the circuit of the obstacle sensing device (31′) can be kept closed in this time period. After review by the inventors, a simpler and more effective means is found to achieve this purpose, so the present invention is accomplished therewith.